This invention relates to microwave antennas for intrusion alarm systems and to improvements in alarm systems of the microwave type.
It is known to monitor the presence of intruders into a room by detecting disturbances in a microwave field generated by a microwave transceiver and antenna unit. The antenna is of the horn type and consequently the microwave radiation pattern is basically directional. Thus the detecting unit is normally located in a corner of the room to be monitored and the horn aperture is directed toward the farthest corner of the room. A major disadvantage of such prior systems is that best results are obtained in rather long and narrow rooms otherwise there can be unwanted detection of circulation taking place outside of the monitored room. It is also known that horn detectors do not normally detect peripheral movements; they can only "see" displacements that have a radial component and that take place in front of the horn antenna.